The overall goal of this project is to define the factors underlying the blunted growth hormone (GH) response to pharmacological stimulation that is characteristic of children and adults with depression and to utilize this information to identify neural systems which may underlie the development of affective disorders. Blunted stimulation of the anterior pituitary hormone, GH, after a number of pharmacological stimuli, occurs in patients with depression throughout the lifespan, and the blunted GH response is one of the most consistent physiological measures documented in children and adults with depression. Children with depression tend to exhibit less exploratory behavior and more inhibited behavior in a variety of psychological tests. We are performing the current pilot study to determine if the monkey will serve as an appropriate model for studying affective disorders and the biological markers, such as GH response, that are associated with certain affective states. Therefore, this project is quantifying the behavioral characteristics of young monkeys with regard to exploratory versus inhibitory behavior, and quantifying GH responsiveness to stimulation, and then assessing the degree of correlation between these parameters. Over the summer of 1996 we developed 4 behavioral testing paradigms, based directly on behavioral testing paradigms used in children to assess these characteristics. The tests we have developed include (1) a playroom test, (2) startle response to a novel stimulus (a toy car), (3) response to approach by a stranger and (4) response to a novel food. We also have developed a procedure for testing GH responsiveness to stimulation which involves administration of 5 ug/kg of GH-releasing hormone (GHRH) plus 10 ug/kg of clonidine. In 1997 we tested 50 monkeys and we have found a great deal of heterogeneity in both behavior and GH responsiveness.